Excretion
Exam-ready definition
The removal from organisms of the waste products of metabolism (chemical reactions in cells including respiration), toxic materials, and substances in excess of requirements.
How this is marked
The paying words are 'waste products of metabolism' (or 'chemical reactions in cells') and 'toxic' and 'in excess of requirements'. The mark students drop most is confusing this with egestion: examiners want you to know excreted substances were made inside cells, not just passed through the gut. Carbon dioxide from respiration and urea from the liver are the classic examples to name.
In an exam answer
Asked to define excretion: 'Excretion is the removal of the toxic waste products of metabolism, such as carbon dioxide and urea, and substances in excess of requirements, from the body.'
Full topic guide: Excretion in humans
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